Abstract As mineral exploration becomes increasingly difficult, costly and competitive, success is essential; there is no room for waste or inefficiency. Exploration must be truly cost effective. The present book is concerned ultimately with the interpretation of geochemical surveys. However the data to be interpreted are the product of the field survey and thus only as good as the work that went into these earlier phases. The truism "garbage in—garbage out" is as relevant here as anywhere. These are independent yet interdependent functions. Failure to execute one step correctly will negate all efforts in the succeeding steps. By and large the function that is most costly, and certainly most difficult to repeat, is the field survey. Any deficiences at this stage will have fatal effects on the remainder of the project. Analysis of the samples is, indeed, costly and an area of necessary concern. However, if samples have been collected properly it is not unreasonable to suppose that they can be reanalyzed should this be deemed necessary or useful. Ultimately interpretation, provided that sampling and analysis are reliable, is an exercise that can be repeated many times using a variety of techniques or models depending on supplementary information available and the skills and prejudices of various geologists or geochemists. The design and execution of a geochemical survey is thus crucial to its success. Surveys can be, and are, optimized to find specific targets in particular environments. Such fine tuning requires an understanding of applied geochemistry, knowledge of the environment in which the survey will be carried out and an appreciation of the target being sought. Before considering these points in more detail, it is worth defining the nature of a geochemical survey in more general terms and establishing clearly the role of the survey in an exploration program. The basic premise of exploration geochemistry is that the systematic sampling and analysis of naturally occurring materials will reveal features indicative of the presence of potentially economic mineralization. This is a deceptively simple statement for it begs the questions—what materials should be sampled?; how and for what entities should these samples be analyzed?; and what features will be revealed? We will consider these points in more detail in later sections. The key wording here is “systematic sampling and analysis.” Regular and consistent application of a technique across a property should produce a common database, a synoptic picture of the distribution of elements or compounds, that will meet